Strongyloides stercoralis is an important intestinal parasite of man, primates, and dogs that causes a spectral disease, ranging from a well-tolerated, self-limiting infection to an uncontrolled, often fatal autoinfection in immunosupressed individuals. The filariform infective larva is environmentally resistant, initiates skin penetration and migrates to the intestine, where it can remain for 40 years in humans. To better understand these processes, we are studying the sensory neuroanatomy and oral structures presumably involved in penetration and feeding. These structures are large, and therefore must be reconstructed from serial sections. IVEM simplifies this process by allowing us to use thicker sections than we could use in conventional TEM. Three-dimensional computer reconstructions made from semi-thick serial sections photographed in the IVEM and reconstructed using programs installed in this Resource are revealing structures similar to those seen earlier in C. elegans. However, we now have seen important differences between Strongyloides and C. elegans. All of the 16 labial sensilla in Strongyloides appear to be closed to the environment: the amphidial pores are the only chemosensory organs open to the exterior. These observations may explain the special resistance of this organism to the environment. This project has become a model for several other, similar projects in this laboratory, using this Resource, and these are included under this global project. 8-31-96